package org.litesoft.codec;

import org.litesoft.charstreams.*;
import org.litesoft.commonfoundation.annotations.*;

public class PrimitiveLongCodec
{
    public static final PrimitiveLongCodec SIGNED = new PrimitiveLongCodec( true );
    public static final PrimitiveLongCodec NON_NEGATIVE = new PrimitiveLongCodec( false );

    private final boolean mSignedValuesOK;

    private PrimitiveLongCodec( boolean pSignedValuesOK )
    {
        mSignedValuesOK = pSignedValuesOK;
    }

    public void encode( @NotNull CharSink pCharSink, long pValue )
    {
        if ( (pValue < 0) && !mSignedValuesOK )
        {
            throw new IllegalArgumentException( "Negative values not supported: " + pValue );
        }
        new Encoder( pCharSink, pValue ).encode();
    }

    public long decode( @NotNull CharSource pCharSource )
    {
        return new Decoder( pCharSource ).decode();
    }

    private static final int NEGATIVE_1ST_CHAR_BIT = 16;
    private static final int NON_NEGATIVE_1ST_CHAR_BIT = 0;

    private static final int SIGNED_1ST_CHAR_MASK = 15;
    private static final int SIGNED_1ST_CHAR_FACTOR = 16;

    private static final int UNSIGNED_1ST_CHAR_MASK = 31;
    private static final int UNSIGNED_1ST_CHAR_FACTOR = 32;

    private static final int MORE_BIT = 32;
    private static final int MORE_MASK = 31;
    private static final int MORE_FACTOR = 32;

    private class Common
    {
        protected final int mFirstCharMask;
        protected final int mFirstCharFactor;

        protected Common()
        {
            if ( mSignedValuesOK )
            {
                mFirstCharMask = SIGNED_1ST_CHAR_MASK;
                mFirstCharFactor = SIGNED_1ST_CHAR_FACTOR;
            }
            else
            {
                mFirstCharMask = UNSIGNED_1ST_CHAR_MASK;
                mFirstCharFactor = UNSIGNED_1ST_CHAR_FACTOR;
            }
        }
    }

    private class Encoder extends Common
    {
        private final CharSink mCharSink;
        private long mValue;

        private Encoder( CharSink pCharSink, long pValue )
        {
            mCharSink = pCharSink;
            mValue = pValue;
        }

        public void encode()
        {
            if ( mSignedValuesOK && (mValue < 0) )
            {
                if ( Long.MIN_VALUE == mValue )
                {
                    mCharSink.add( SixBitCodec.encode( NEGATIVE_1ST_CHAR_BIT ) ); // Record as '-0'
                }
                else
                {
                    mValue = -mValue;
                    encode( NEGATIVE_1ST_CHAR_BIT );
                }
                return;
            }
            if ( mValue < mFirstCharFactor )
            {
                mCharSink.add( SixBitCodec.encode( (int) mValue ) );
            }
            else
            {
                encode( NON_NEGATIVE_1ST_CHAR_BIT );
            }
        }

        private void encode( int pNegativeBit )
        {
            int bits = extractBits( mFirstCharMask, mFirstCharFactor );
            mCharSink.add( SixBitCodec.encode( bits | pNegativeBit ) );
            while ( mValue > 0 )
            {
                bits = extractBits( MORE_MASK, MORE_FACTOR );
                mCharSink.add( SixBitCodec.encode( bits ) );
            }
        }

        private int extractBits( int pBits, int pDivisor )
        {
            int rv = (int) (mValue & pBits);
            if ( (mValue /= pDivisor) > 0 )
            {
                rv |= MORE_BIT;
            }
            return rv;
        }
    }

    private class Decoder extends Common
    {
        private final CharSource mValue;
        private boolean negative;

        private Decoder( CharSource pValue )
        {
            mValue = pValue;
        }

        public long decode()
        {
            int bits = SixBitCodec.decode( mValue.getRequired() );
            negative = mSignedValuesOK & ((bits & NEGATIVE_1ST_CHAR_BIT) != 0);

            long result = (bits & mFirstCharMask);
            for ( long zMultiplier = mFirstCharFactor; (bits & MORE_BIT) != 0; zMultiplier *= MORE_FACTOR )
            {
                bits = SixBitCodec.decode( mValue.getRequired() );
                result += (bits & MORE_MASK) * zMultiplier;
            }
            if ( !negative )
            {
                return result;
            }
            if ( result == 0 ) // '-0'
            {
                return Long.MIN_VALUE;
            }
            return -result;
        }
    }
}